Evaluation of Some Pollution at Manzala Lagoon: Special Reference to Medical Importance of Mollusca in Egypt

Several factors are considered in affecting the ecology of snails and other intermediate hosts of diseases, hence their focal and seasonal distributions. These include physical factors such as water current, temperature, turbidity, transparency and distribution of suspended solids, chemical factors such as ion concentration and dissolved gases in water as well as biological factors such as availability of food, competition and predator-prey interactions [1,2]. However, the importance of different ecological factors vary significantly from one ecological zone to the other and even from one water body to the other, suggesting local investigations to identify important factors in each zone or water bodies [2-5]. Many studies concerned with the ecology and population dynamics of gastropods which play an important role in transmitting diseases to man and his livestock have been conducted by Abd El-Malek [6]; Dazo et al. [3]; Barbosa and Barbosa [7]; Utzinger et al. [8]; Kloos et al. [9]; Karimi et al. [10]; Cañete et al. [11] Kazibwe et al. [12] and Mostafa [13]. These studies have led to general opinion; that the development of an effective strategy of integrated control requires the study of population dynamics of the intermediate hosts and its relation to environmental factors. Population dynamics of these animals depend on the physical geography of a given region, also land contours, soil composition; hydrography and climate all have effect on snail population dynamics [14].


Introduction
Several factors are considered in affecting the ecology of snails and other intermediate hosts of diseases, hence their focal and seasonal distributions. These include physical factors such as water current, temperature, turbidity, transparency and distribution of suspended solids, chemical factors such as ion concentration and dissolved gases in water as well as biological factors such as availability of food, competition and predator-prey interactions [1,2]. However, the importance of different ecological factors vary significantly from one ecological zone to the other and even from one water body to the other, suggesting local investigations to identify important factors in each zone or water bodies [2][3][4][5]. Many studies concerned with the ecology and population dynamics of gastropods which play an important role in transmitting diseases to man and his livestock have been conducted by Abd El-Malek [6]; Dazo et al. [3]; Barbosa and Barbosa [7]; Utzinger et al. [8]; Kloos et al. [9]; Karimi et al. [10]; Cañete et al. [11] Kazibwe et al. [12] and Mostafa [13]. These studies have led to general opinion; that the development of an effective strategy of integrated control requires the study of population dynamics of the intermediate hosts and its relation to environmental factors. Population dynamics of these animals depend on the physical geography of a given region, also land contours, soil composition; hydrography and climate all have effect on snail population dynamics [14].
The main objective of this study is the preparation of a sustainable development plan for the area, and elaboration of methodological procedures for implementation and reliability. One of the specific objectives of the Manzala Lagoon study is to define the environmental state and to identify protection policies, where the freshwater molluscs have been known to play significant roles in the public and veterinary health and thus need to be scientifically exploring more extensively.
Urban and industrial activities would enumerate impacts, sources of pollution, urban solid waste storage, industrial waste and their storage, chemical pollution of water and air, urban sprawl. An adequate reference would be made to relevant Infrastructures of direct and indirect negative impacts/risks on the environment, mitigation and compensation actions, future consequences.
This study is intended to produce data on the distribution seasonal variations in densities of gastropod molluscs at Manzala Lagoon with emphasis on environmental factors affecting them.

Materials and Methods
The recent bottom sediments were collected seasonally from seventeen selected stations in the Manzala Lagoon along selected profiles in order to cover his whole area ( Figure 1). The sampling was commenced in winter (2010) and continued to summer (2011). The bottom sediments were collected from Manzala Lagoon using a grab sample (Ekman type), which was immersed to depth ranging between 85 centimeters and 160 centimeters. The bottom water temperature was measured by regular mercury thermometer up to 5°C, as well as the heavy metals analyses, the chlorsity and organic matter were determined for bottom sediments in the Manzala Lagoon in different seasons (Tables 1-5).

Sites of Investigation
The collecting of snails was carried out in seventeen sites at Manzala Lagoon ( Figure 1). Freshwater mollusca have been known to play significant roles in the public and veterinary health and thus need to be scientifically exploring more extensively [15]. About seven species of freshwater gastropods are reported to act as intermediate hosts for the diagnostic trematode parasites and among Prosobranchs, members of the family Pilidae and Thiaridae were recorded to harbor larval trematodes [16]. Meanwhile, only one genus of saline water was recorded at the area of study (Cerithium).

Manzala lagoon
Manzala lagoon (formerly known as Lake Tanis) is the largest brackish water body (~1071 km 2 ) located in the northeastern shoreline of the Nile Delta, and lies between 31° 10" and 31° 40" latitude and 31° 80" and 32° 25" longitude. It is bounded by the Mediterranean Sea to the north, Port Said to the northeast, the Suez Canal to the east, El-Dakahlia Governorate on the southwest, El-Sharkia Governorate on the south, and Damietta on the west (Figure 1). It is a shallow brackish water lagoon, with a depth ranging between 0.7 and 1.5 m [17].
The lagoon has a maximum length of 64.5 km and a maximum width of 49 km. The area of the lagoon has been reduced to 1200 km 2 by 1980 as a result of land reclamation [18]. The original area of Manzala Lagoon was more than 1700 km 2 in 1900 [19].
Manzala Lagoon is connected to the Mediterranean Sea through the outlet of Boughas Al-Gamil (12.5 km west of Port Said) and strait of Sheikh Ali (25 km northeast of Damietta). It connects with Suez Canal through a small navigation canal known as El-Gaboaty Canal. These openings supply the lagoon with water and fishes. The western and southern shores have many inlets by which great amounts of water drain into the lagoon. The most important drains are Bahr El-Baqar, Hadous, Ramsi, Al-Sirw, Abu-Garida and Faraskur. The lagoon has been missing administrated during the last few decades where it acts as reservoir for wastes fluxing from various directions. Effluents from more than 200 sewage disposal units and about 80 industrial facilities pour into the lagoon [20].
Many drains transport water from the eastern delta to the lagoon, carrying large amounts of particulate matter, nutrients, bacteria, heavy metals, and toxic organics. Methane and hydrogen sulfide bubble up to the surface, releasing greenhouse gases. Therefore, poor water quality of lagoon threatens wildlife, ecosystems, and the health and livelihood of people in the area, while polluting Mediterranean Sea.

Climate and current regime
The lagoon water attains minimum temperature of 15°C during January-February gradual increase in these values is observed during late winter and spring. They reach the maximum during July-August ( Table 1). The maximum values attain 34°C at the beginning of August.
The surface current was measured and listed in Table 1. During winter season a weak current was recorded only in south western part of the lagoon with an average 29 cm /sec. Generally, the maximum velocity of the surface current was recorded in summer season. Rainfall occurs only in winter (November to March), while the summer months are dry. Winds usually blows from north eastern direction in summer.

Water chloroisty
Chlorosity was measured at each station by arganometric method as recommended in American Public Health Association. The data derived from measurements are listed in Tables 2-5. During winter season, the chlorosity gradient increases toward the opening of Boughas El-Gameel, and varied from 886.3 mg/l to more than 3000 mg/l at the northern part of the lagoon. During the spring the chlorosity varied from 709 mg/l to 18345 mg/l. During summer season, the chlorosity varied from 15 mg /l to 5034 mg/l. During autumn season the chlorosity of the bottom water ranged from 709 mg/l to 4431 mg/l. It is clear that the maximum value of the water chlorosity was recorded in spring season while the minimum value was recorded in winter season. The obvious increase in the water chlorosity during spring may be due to an increase in temperature and consequently increasing in evaporation. From Tables 2-5 the chlorosity increases toward the inlet of Boughas Al-Gamil at the north portion of the Manzala Lagoon (station 11, 12, 13, 15, 16 and 17).

Pollution sources
Agricultural drainage water: Manzala Lagoon is influenced by fresh water runoff from the land via drains and canals. A total of 3.7 billion cubic meters of water (mostly from agricultural drainage) flow annually into Manzala Lagoon from nine major drains and canals. Bahr El-Bakar Drain has the most polluted drain discharges into Manzala Lagoon. Apart from being the largest consumer of water, agriculture is also a contributor to water pollution. Drainage water seeping from agriculture fields is considered non-point sources of pollution. Moreover, these non-point sources of pollution may also influence the groundwater quality. Major pollutants in agricultural drains are salts; nutrients (phosphorus and nitrogen); pesticide residues (from irrigated       More than often, the drains have strong odor due to generation of H 2 S. People living along the banks of the drains are exposed to chemical pollutants [21]. The drains wastewater pollutants affect the human health because they use the drain waters in their life needs. The Bahr El-Bakar drain receives untreated and primary treated wastewater from east Cairo region along its total length of approximately 170 km and discharges into Manzala Lagoon.

Heavy metals
The studies on heavy metals in rivers, lakes, lagoon, fish and sediments have been a major environmental focus especially in the last decades. Sediments are important sinks for various pollutants like pesticides and heavy metals and also play a significant role in the remobilization of contaminants in aquatic systems under favorable conditions and in interactions between water and sediment [22][23][24][25].

Iron:
The minimum average value of iron was recorded during autumn (5.41 mg/g). It increased gradually during winter (5.83 mg/g) and reached (5.86 mg/g) during spring and summer. Concerning sampled stations, the maximum annual average values of iron were recorded at stations No.1, 2, 5 and 12 being 6.44 mg/g, 6.38 mg/g, 6.17 mg/g and 6.41 mg/g respectively (Tables 2-5).

Zinc:
The maximum average value of zinc was recorded during summer (79.17 µg/g). It decreased gradually during autumn and spring (69.08 µg/g, 62.17 µg/g respectively). It reached its minimum average value during winter (60.17 µg/g). Concerning sampled stations the maximum annual average values of zinc were recorded at stations 1 and 5 being 143.75 µg/g and 100.25 µg/g respectively (Tables 2-5).
Copper: The highest average value of copper was recorded during summer (186.58 µg/g). It decreased gradually during autumn and winter (154.75 µg/g, 136 µg/g respectively). It reached its lowest average value during spring (123.5 µg/g). Concerning sampled stations the maximum annual average values of copper were recorded at stations 1 and 7 being 308.5 µg/g and 213 µg/g respectively (Tables 2-5).

Organic Matter
From Tables 2-5 it was found that the organic matter content in the sediments collected in winter season ranges from 0.12% and 0.41% with an average 0.26%, while in spring season it varies from 0.15% and 0.36% with an average 0.25%. During summer season the organic matter content varies from 0.1% to 0.5% with an average 0.23%, while in autumn season it varies from 0.16% to 0.35% with an average 0.27%. The area characterized by low organic matter contents is located at southern part of the lagoon, while the relatively higher organic matter contents were recorded in the east and west of the lagoon.

Results
A total of 11 Genera of gastropod species were recorded in the Manzala Lagoon; belong to 17 species. A separation of freshwater and marine species is clearly evident.  (Tables 6-9) [28][29][30].
The total numbers of snail ( Figure 2) showed its highest value during autumn (representing 39.60%), followed by summer (25.70%), winter (18.80% (then spring (15.90%), whereas the least numbers were recorded in spring (15.90). The present result agrees with Karimi et al. [10] where they found that late summer and autumn had the optimal temperature required for breeding and reproduction of the collected snails. The April, May and June (the spring months) showed the lowest density of snails in Manzala Lagoon, while the highest density was recorded during January and February (the autumn Months) [31].
The obtained data revealed that the sediments of the western and southern sides (station 1, 2, 3, 4, 5, 7, 10 and 14) of Manzala Lagoon are characterized by very low species diversity indices. This very lowering in species indices can be considered as a response to pollution, and consequently act as a pollution indicator.
The highest average value of heavy metals was recorded during summer, where the maximum annual average values of these metals were recorded at stations 1, 2, 3 and 5.

Summary and Conclusions
Coastal area, particularly lagoons have been described in the international literature as typical locations where sediment-associated pollutants can be accumulate due to anthropogenic activities. Biological communities appear to provide a direct means of observing the impact of contaminants.
The present study has been conducted in order to evaluate the degree of pollution and its influence on the mollusca of the Manzala Lagoon, as the gastropods Bulinus (Bulinus) truncatus, Bellamya unicolor, Biomphalaria alexandrina, B. glabrata, Melanoides tuberculata and Lymnaea (Pseudosuccina) columella are of considerable importance because they acting as a host for Cercaria pusilla, Fasciola hepatica, Schistosoma mansoni and Schistosoma haematobium disease vectors. The latter two can cause Schistosomiasis transmission (Bilharzia). This work is the first of its kind for the Manzala Lagoon.
The largest consumer of water, agriculture is also a contributor to water pollution. Drainage water seeping from agriculture fields is considered non-point sources of pollution. These non-point sources are, however, collected and concentrated in agricultural drains and become point sources of pollution for the Manzala Lagoon. Major pollutants in agricultural drains are salts; nutrients (phosphorus and nitrogen); pesticide residues (from irrigated fields), pathogens (from domestic wastewater), and toxic organic and inorganic pollutions (from domestic and industrial sources).